Synthesis of chondromucoprotein by chondrocytes in suspension culture

Proteoglycans synthesized by fetal guinea pig chondrocytes in culture

Short term cultures were carried out with chondrocytes and tissue fragments from fetal guinea pig epiphyseal cartilage. Proteoglycans were isolated from these cultures and their properties were compared with those of proteoglycans from adult hyaline cartilage. It was concluded that the proteoglycans synthesized in culture were essentially similar to those present in cartilage matrix in vivo. The authors therefore suggest that fetal guinea pig chondrocytes cultured in monolayer or as aggregates in suspension constitute a useful system for the study of synthesis and secretion of proteoglycans.

Stimulation of extracellular matrix synthesis in the developing cornea by glycosaminoglycans

Previously, it was demonstrated that the embryonic corneal epithelium produces the chondroitin sulfate and heparan-sulfate-like compounds and the collagen of the primary corneal stroma. Synthesis of all of these extracellular materials is greatly enhanced in vitro when isolated epithelium is grown on collagenous substrata instead of Millipore filters. We report here that chondroitin sulfate, heparin, and heparan sulfate added to the culture medium at a concentration of 200 mug/ml enhance the synthesis by the epithelium of chondroitin sulfate and heparan-sulfate-like compounds 2-fold, whether or not collagenous substrata are employed. Collagen synthesis is unaffected by adding glycosaminoglycan to the medium. Chondroitin sulfate proteoglycan (chondromucoprotein) has the same stimulatory effect as chondroitin sulfate, but dermatan sulfate and hyaluronate have no measurable effect on glycosaminoglycan production by epithelial cells. Keratan sulfate however, seems to depress glycosaminoglycan synthesis. Thus, in this system, only sulfated polyanions like those produced by the corneal epithelium have a stimulatory effect on glycosaminoglycan synthesis. The results are discussed in terms of how the tissues of the cornea (epithelium, endothelium, keratocytes) may interact by changing the composition of the stromal extracellular matrix.

Stimulation of chondromucoprotein synthesis in chondrocytes by extracellular chondromucoprotein

Chondrocytes in suspension culture preserve their differentiated state, as expressed by a high rate of chondromucoprotein synthesis. Purified chondromuco-protein added to a suspension of cultured embryonic epiphyseal cartilage cells stimulates the rate of synthesis of chondromucoprotein at concentrations up to 2 mg/ml. The stimulation involved synthesis of the entire molecule since incorporation of labeled serine (into core protein), glucosamine, acetate, or sulfate was increased. Neither the amount of synthesis of total protein nor that of collagen was increased. No elevation of xylosyltransferase and N-acetylgalactosaminyltransferase activities was observed. The stimulation was produced by several other polyanionic substances. No evidence was found of the entry of chondromucoprotein into chondrocytes under the conditions of the experiments. Mild trypsinization lowered the response to added chondromucoprotein and decreased the endogenous rate of chondromucoprotein synthesis. Incubation of cells after trypsinization results in restoration of the rates of chondromucoprotein synthesis. The endogenous, as well as the stimulated, rate of chondromucoprotein synthesis varied with the density of chondrocytes in culture. It is suggested that the rate of chondromucoprotein synthesis may be partially controlled by cell surface receptors.